Non-curling gummed paper and method of making



Oct. 19, 1965 B. AsNEs 3,212,924

NON-CURLING GUMMED PAPER AND METHOD OF MAKING Filed July 6. 1962 INVENTOR. fZ/'hmlz #Kiwi United States Patent Ofiice 3,212,924 Patented Oct. 19, 1965 3,212,924 NON-CURLING GUMMED PAPER AND METHOD F MAKING Benjamin Asnes, Framingham, Mass., assignor to Dennison Manufacturing Company, a corporation of Nevada Filed July 6, 1962, Ser. No. 208,076 Claims. (Cl. 117-122) This is in part a continuation of Serial No. 692,253, filed October 25, 1957, and now abandoned.

This invention relates to gummed sheet material, that is, sheet material having a coating of dry adhesive which can be moistened with water to develop an adhesive tackiness which permits the sheet to be attached to another surface. Such coated sheets are common articles of commerce, gummed labels and postage stamps being common examples. Adhesives of this nature are commonly called remoistenable adhesives, glue or gum and these terms are herein used to include any normally non-tacky adhesive which can be activated with water.

Gummed sheet materials of this character have been troublesome in use because of their tendency to curl or roll up with changes in relative humidity due to the uneven expansion and contraction of the adhesive coating and of the backing sheet. This problem is particularly troublesome in gummed sheets which receive printing for labels and the like which have to be run through printing presses in controlled registration therewith. This difficulty has necessitated printing rooms with controlled relative humidity.

A number of expedients have heretofore been attempted to correct this problem but with only partial success. The most usual expedient adopted has been to break up the coated adhesive into small sections by drawing the coated sheet under tension over variously disposed edges. This method is only partially effective and requires an additional and troublesome operation. Another expedient used has been the inclusion of resilient fillers to minimize the differential effect of the expansion and contraction. This method is also only partially effective and increases the cost.

A recent expedient is disclosed in United States Patent No. 2,793,966. This method involves the dispersion of minute particles of solid water-reactivatable adhesive in a solvent solution of a second gum which is also water soluble. The solvent used for the dispersion dissolves the second or carrier gum which is present in a minor proportion when compared with the water-reactivatable adhesive, but in which the latter is not soluble. After coating and drying, the minute solid particles of water-reactivatable adhesive are presumably discontinuous in a matrix of the second gum. This method produces a gummed sheet of superior flatness but introduces its own problems. An important problem with this method is the necessity for obtaining the water-reactivatable adhesive in a very fine particle size, usually less than one mil. Such materials, being adhesive and moisture-sensitive, are extremely difficult to grind and maintain in this small particle size. Also this method requires substantial amounts of the second or carrier gum which is quite expensive when compared with the usual water-sensitive adhesive.

The principal object of this invention is to provide superat gummed sheet material, together with a method and coating composition for making the same which will remain substantially flat even after repeated changes in relative humidity. Further objects are to provide superat gummed sheet material having an adhesive layer which is firmly bound to the carrier sheet, which will not block or adhere to superposed sheets when stacked with other sheets of like material, which is readily activated with water, which is easily prepared, and which is relatively inexpensive when compared with previous methods.

In accordance with this invention the improved superat gummed sheet material of the water-remoistenable type comprises a sheet having on one side thereof a potentially adhesive dry fihn which when moistened with water will adhere to a surface, said film comprising in discontinuous phase a multiplicity of minute particles of water-soluble gum and in continuous phase of a resinous film-forming binder joining said particles together and to the sheet, said binder being substantially insoluble in water but suiciently open to permit quick activation of said particles by water. The particles of water-soluble gum should comprise a major portion of the total mass of the film and the ratio of gum to binder should be at least about 4 to 1 by weight. Suitable binder materials are substantially water-insoluble polyvinyl ester copolymer, polyvinyl chloride, butadiene-styrene copolymers, and polymers of acrylic esters. The preferred and substantially superior binder is water-insoluble polyvinyl acetate copolymerized with a small proportion of material of the crotonic or maleic type. While the water-soluble gum is in discontinuous phase, the particles do adhere to each other to a slight extent and those in the inner stratum of the coating adhere directly to the carrier sheet. Indeed if the continuous phase is dissolved from the coating, the gum remains as a self-supporting porous structure. Likewise if the gum is extracted from the film, the resinous binder remains as an open, spongelike structure.

The above superliat gummed sheet material is made by a method which comprises dissolving a substantially water-insoluble binder in a solvent or mixture of solvents which is incompletely miscible with water, dissolving a water-reactivatable gum in water, dispersing the water solution in the binder solution, coating the resulting composition on the sheet, and drying. After the coating has been dried the exposed surface of the carrier sheet should be treated under tension, according to techniques well known in the prior art, to equalize the contraction caused by wetting the coated side.

In a further aspect the present invention includes a coatable composition for preparing water-remoistenable gummed sheet material comprising a dispersion of a water solution of water-reactivatable gum dispersed in a solution of substantially water-insoluble, resinous, filmforming binder in a solvent incompletely miscible with water, said gum exceeding by weight the amount of the binder.

To the naked eye the coatings of the present invention appear smooth and substantially homogeneous. However, microphotographs show rather clearly that the coatings, after drying, have particles of Water-reactivatable adhesive embedded in a water-insoluble binder matrix. These particles are available to water as is illustrated by the ease with which the film is made tacky by moistening and by the fact that micro-photographs of samples taken after prolonged immersion in water show that most of the gum particles are leached out by the water. The use of water-insoluble binder thus does not prevent the reactivation of the gum while providing resistance against the washing away of the coating and permitting the use of thinner coatings.

This invention can be illustrated by the following examples where al1 parts are parts by weight.

EXAMPLE I Dissolve polyvinyl acetate iciopolymerized with a srnallfpr-oportion of material of the crotonic or 'maleic type (C3V-10 of the Shawinigan Products Corp.) 25 in:

Toluol 150 vlsoprolpanol 50 A`Ethyl acetate Santicizer E15 (phthalate etbyleglycolate la plasticizer ofthe Monsanto OhemicalCo.) after a clearsolution is obtained :add:

17% :ammonia solution 8 and stir Well.

Bone .glue 125 iDextrin 365 :Water 210 Add :ammonia (28%) Vto the vlwatervsolution ofthe gum base (B) until it is slightly:talk-aline then add BL-slowly to lA while stirrin g vigorously and then thin to ra good. coat- Iing viscosity by adding 20 to 30 parts of ethyl acetate to the dispersion Further examples illustrating a variety of water-insolurble resins -Whiclh .can be used are'shown'bytheloll-owing:

Example N o Animal l Dextrin-.

Pliolite Latex #170 is a 30% emulsion of a butadiene-styrene polymer of the Goodyear Tire & Rubber/Co.

Geon' 200 x 20" is a'polyvinyl chlorid'eresinof the B. F..Goodrich Co.

Aeryloid B66 is 21.40% solidsintoluol oan acrylate of theRohma 55 Haas Co. CA1vexi(4cc417).is a 50% 'vinyl emulsion ofthe'Calverton Chemical orp.

The dispersione in the examples in the above formulations iare Amade in substantial-ly the same manner as that shown in Example AI. The binder is dissolved-in the solvents and the vgum adhesive is separately-dissolved in -Waterl The water solution is Ithen slowly added tothe solvent solution with rapid agitation. In all ofthe examplesV given, except .Example :6, a` slightly alkaline dispersion is more stable. Ammonia or alkali can be-fused with ammonia being preferred. Alfter lcoating anld drying the eoiatings become slightly acid. Example 6, Ailvex, is acid thnoughout. The coatings made using the vinyl acetate-maleic anhydride copolymers (having a-pfreponder- .ance `of the vinyl acetate) Ias the continuous pbase binder are substantially superior. Another commercial example ef this type of resin is Polyco 541'of the American Polymer i orp.

The ratio `of water soluble gum to binder can vary between .about 4:1 and 12:11 as shown :by the following examples:

'Ilhe dispersion technique is critical in making coatings according to this invention. (Ilhe wlater-neactivatable adliesive or .gum must make upa major portion of the d-ried iilm and must be dispersed as a -water solution in a solvent solution of a water-insoluble binder. The dispersion must be a dispersion of the water in oil type with the solvent phase as the continuous phase and the vvater phase Ias the '..disoontinuous For this purpose the solventsV used to dissolve the binder'must be incompletely miscible Witlh water. v Solvents :dan 'be used for this purpose which are complete- "ly Water-immiscible, however limited miscibility for the solvent 'helps to make :a stable dispersion. Suc-l1 limited miscibility can be obtained by using a mixture of solvents, some of whidh are miscible withwater and some tof which Iare immiscible `with-water. -iLimited misci'bility can also be obtained with a :solvent which lhas ali'mited miscibility with water by using amounts which are in excess of the :amount which `would be misoiblewwith the quantity of water used. Suilicient solvent must be used to hold the dispersion tothe water in 'oil type. :Ear at least 25% solvent. by volume has been required for this purlpose. Whether the solvent comprises Ia single liquid or a mixture of liquids the only requirement is that it be suiiiiciently immiscible with water to keep the water solution in `dispersed, phase.

The continuous phase binder must adhere to the .gum and to .the Abase ion which it is coated. The binders of the present invention are substantially water-insoluble which provides increased resistance against washing away of the :gumming when ,-rnoistened liberally [and permits @lighter coating Weights and the use of cheaper and more soluble gums such as dex-trins. While the binder is waterinsolufble, 'the' water-reactivatable adhesive is readily accessible to remoistening and can be leadhed almost completely from the dried coating :by immersion in water. Apparently the binder structure is quite fopen and porous. lIt is believed that this lopen structure is obtained by t'he evaporation of water land solvents ias the coating is dried. "Io this end Athe use of the water-reactivatalble adhesive in a water solution rather than las a dry powder is a decided advantage. It has 'the further .advantagesiof better bonding to the supp ort, permitting the ruse of lhigher amounts of water-soluble adhesive, increased speed of activation,

' loiwer'fcost, and because it obviates lthe need for grinding the igum'into very line particles as taught in the prior art.

Some plasticity is desirable in the binder 11e-sin land it 'thas been found desirable to add plasticizers to most lof the resins used for this purpose. ln' addition tothe plasticizers shown in the examples, plasticizelrs Well known v for lthe particular resins can also be used.

To increase quick-tack still further without jeopardizing atness it is obviously desirable to increase the ratio of glue to resin without making a more'nearly Continous glue lm or, put another way, to descrease the proportion of resin and yet have enough resin present to keep the glue globules from coalescing completely. Furthermore, flatness could actually be'improved if less water were introducedinto the system asthe glue-resin ratio is increased. As explained above, to avoid the dusting which occurs when dryglue is used in .fa proportion to resin higher than 4:1, a glue solution is emulsiied in the resin solution. But

if this glue solution is more than 50% glue it is too viscous to emulsify. Thus, as glue-resin ratio exceeds 6:1 curl begins to increase because it is necessary to add so much water with the glue that the glue globules tend to coalesce too much.

An improvement on the foregoing consists in dissolving water-activatable gum in water to form a water solution of gum, dispersing discrete particles of water-activatable gum in a binder which is incompletely miscible with said water solution and in which said gum is not readily soluble, and dispersing the water solution in said binder to form an emulsion comprising globules of gum in addition to said particles, coating the emulsion on a sheet, and drying the coating while permitting said globules to coalesce partially to form a honeycomb structure of partially coalesced gum particles, the aforesaid binder forming a barrier which prevents said globules from coalescing completely. Before dispersing the water ysolution in the binder an emulsifying agent should be added to the water solution.

Typical examples for coating paper .are as follows, all parts being by weight. In these examples A is the binder solution, B the discrete particles of adhesive, C the water solution and D the emulsifying agent. The carrier and water solutions may also be formulated as in any one of the Examples l to 9.

Examples 10 11 12 13 14 77. 0 50.0 75.0 25. 0 50. 0 75. 0 100.0 100.0 2.0 2.0 er 2.0 2. 0 Ratio, Adhesive: 33:1 12:1

Preferred formulas Examples 15 16 17 18 C3V10 12. 5 Santicizer 141. 4. 5

0. 0 108. 5 108. 5 108. 5 108. 5 A.-. Ethyl Acetate-. 2. 0 Isopropanol. 9. 5

olu 20. 0 20. 0 20. 0 Ethyl Acetate 20. 0 20.0 20.0 B Dextrin (Dry) 60. 0 60. 0 60. 0 30. 0 Animal Glue (Dry 30.0 Dextriu 15. 0 100. 0 C--. Animal Glue--- 100. 0 85. 0 100.0 Water 125. 0 125.0 100. 0 125. 0 D {NHiOH (Con 5.0 5.0 2. 0 5. (l Water 5. 0 5.0 2.0 5.0 Ratio, Adhesive 12. 8:1 12. 8:1 12. 8:1 12. 8:1

The dry particles of gum should be added to the liquid binder before the water solution of glue is dispersed in the binder. If the dry particles were added to the water solution instead `of the liquid binder the particles would be dissolved by the water solution. If the water solution is emulsied in the liquid binder before the dry particles are added, the dry particles combine with the globules of liquid adhesive to produce the same result as if all the adhesive has been dissolved in the water solution; the emulsifying agent is not adequate to keep the dry particles away from the emulsied globules.

After the water solution is dispersed in the liquid binder and before the coating is dried, some water is absorbed by the dry particles from the water solution. Thus the dry particles become swollen and when the coating dries they also coalesce partially so that they are well anchored and do not tend to dust off and so that the coating may contain a larger proportion of gum to binder without curling. The elapsed time between the aforesaid dispersion and drying may vary widely depending upon the degree of coalescence desired but it is preferably within two hours.

As indicated in the above tabulations, in Examples 12 and 13 the binder solution contains additional toluol. In the ratio of adhesive to binder, the adhesive comprises both the dry particles and the coalesced particles of gum and the binder comprises the resinous portion of the binder solution which does not evaporate in drying the gumming. In Example 13 the ratio of adhesive to binder is 33 to 1 and good results have been obtained with ratios as high as 35 to l, and of course the higher the ratio the better so long as the gummed paper remains flat and does not block. Moreover the higher the ratio of adhesive to binder the better the adhesive phase is bound together and to the backing sheet.

By causing the gum particles to coalesce partially the resulting product is quite diierent from the case where all the particles are applied in dry form and remain discrete. The marked difference between the two products can be demonstrated easily by dissolving out the binder with a solvent which does not dissolve the glue. In the case of the discrete-particle gumming the glue precipitates as powder, while in the partially-coalesced gumming the glue remains as a self-supporting honeycomb structure. Thi-s diierence affords many advantages.

The partially-coalesced product can have a much higher ratio of glue to binder because the glue helps to anchor the coating to the backing. In the discrete-particle product the coating is anchored to the backing solely by the binder and a larger proportion of binder must therefore be used. Glue being less expensive than binder, this affords a substantial saving in cost.

With the same ratio of glue to binder there is better cohesion in the partially-coalesced product than in the discreate-particle product. Whereas particles of glue tend to dust od from the discrete-particle product, the partially coalesced product is free from this objection. This is very important in printing gummed labels. Whereas the discrete-particle product cannot be printed on the gummed side, the partially-coalesced product can be printed on either side. Whereas the dusting of the discrete-particle product tends to clog the type of printing presses, the partially-coalesced product involves no such tendency.

There is better adhesion of the gumming to the backing in the partially-coalesced product than in the discreteparticle product, with the same ratio of glue to binder, this being due to the fact that the glue globules contribute to the adhesion of the gumming to the backing in the partially-coalesced product, whereas the discrete particles of dry glue contribute nothing to this adhesion in the other product.

With the same ratio of glue to binder the partiallycoalesced product has quicker tack than the discreteparticle product. While this is due partly to the higher ratio of glue to binder it is probably due more to the porosity of the binder resulting from the evaporation of water from the glue blobules during the process of manufacture.

The accompanying drawing is intended to indicate the composition of the gumming and not its structure.

It should be understood that this disclosure is for the purpose of illustration only and that this invention includes all equivalents and modications which fall within the scope of the appended claims.

I claim:

1. The method of making a substantially non-curling gummed sheet of the water-remoistenable type which comprises dissolving in a solvent a binder which is substantially insoluble in water, dissolving water-activatable gum in water, dispersing the water solution in the binder solution, coating the resulting composition on the sheet and drying, the ratio of gum to binder being at least 4:1 by weight, and the solvent being sufficiently immiscible with water to keep the water solution in dispersed phase.

2. The method according to claim 1, wherein the binder 7 solvent comprises at least 25% of the liquid by volume in said composition.

3. The method according to claim 1 further characterizedin that said binder is dissolved in a solvent mixture comprising a substantially water-immiscible solvent and a ,solvent having a limited miscibility with water to facilitate the emulsion.

4. Gummed sheet material of the Water-remoistenable type comprisingfa sheet having on one side thereof a dry lm which when moistened with Water will adhere to a surface, said tilm comprising a resinous film-forming binder, and a multiplicity of minute particles of Watersoluble gum adhering to each other and t-o said sheet in a honeycomb structure, said binder being substantially insoluble in water but sufficiently open to permit quick activation of said particles by water.

5. Gummed sheet material according to claim 4 wherein the binder is selected from the group consisting of polyvinyl ester copolymers, polyvinyl chloride, butadienestyrene copolymers, and substantially Water-insoluble polymers of acrylic esters.

6. The method of making a substantially non-curling gummed sheet of the Water-remoistenable type which comprises dissolving water-activatable gum in Water to form a Water solution of gum, dispersing dry particles of water-activated gum in a binder-solution which is incompletely miscible with said water solutionand in which said gum is not readily soluble, and dispersing the water solution in said binder to form an emulsion comprising globules of gum in addition to said particles, coating the emulsion on a sheet, and drying the coating while permittingsaid globules `to coalesce partially to form a honeycomb structure of partially coalesced'gum particles, the aforesaid binder preventing said globules fromv coalescing completely.

7. The method of making a substantially non-curling gummed sheet of the Water-remoistenable type which comprises dissolving water-activatable gum in water to form a Water Solution of gumdispersing dry particles of Water-activatable gum in a binder solution which is incompletely miscible with said water solution and in which said gum isnot readily soluble, anddispersing the water solution in said binder to form an emulsion comprising globules of gum in addition to said particles, coating the emulsion on a sheet, and drying the coating `While permitting said globules to coalesce partially to form a honeycomb structure of partially coalescedgum particles, the aforesaid binder preventing said globules from coalescing completely and, after said Water solution is dispersed in binder and before vsaid coating is dried, absorbing water into said particles from said solution so that they also coalesce partially.

8. GummedV sheet material of the Water-remoistenable type which comprises a sheet having on one side thereof a coating of water-activatable gum particles partially coalesced in the form of a honeycomb: structure, said particles. being withheld from complete coalescence vby a binder which is substantially insoluble in water, the ratio of gum to binder being at least approximately 10:1.

9. Gummed sheet material of the Water-remoistenable type which comprises a sheet having on one side thereof a coating of Water-activatable gumparticles partially coalesced in the form of a honeycomb structure, said particles being interconnected by a binder which is substantially` insoluble in water, the ratio ofgurn tobinder beingl at least approximately 10: 1.

10. Gummed sheet material according to claim l9 wherein the ratio of gum to binder is of the order of 30: 1.

5/57 Davis 117-122 9/63 Prior a 117-122 RICHARD D. NEVIUS, Primary Examiner.l 

8. GUMMED SHEET MATERIAL OF THE WATER-REMOISTENABLE TYPE WHICH COMPRISES A SHEET HAVING ON ONE SIDE THEREOF A COATING OF WATER-ACTIVATABLE GUM PARTICLES PARTIALLY COALESCED IN THE FORM OF A HONEYCOMB STTRUCTURE, SAID PARTICLES BEING WITHHELD FROM COMPLETE COALESCENCE BY A 